1. Field of the Invention
The present invention relates to a photo electro transducer device, and more particularly to a solid-state photo electro transducer device adapted for use in the optical information input for facsimile, digital copier, laser recording apparatus etc. or in the optical reading device for a bar code reader or other character or image reading apparatus.
2. Description of the Prior Art
Along with the general trend for miniaturization of various apparatus, there has recently been observed a marked development, for use in the optical information input for facsimile, digital copier, laser recording apparatus or other character or image reading apparatus, of a photo electro transducer device provided with a so-called elongated photoreceptor face of a size equal or substantially equal to the size of the original image to be reproduced, showing a high image resolution enabling faithful reading of the original image and being still compact in size.
However such photo electro transducer device with an elongated photoreceptor face has a major difficulty in the signal processing circuits to be used in combination with the photo electro transducer unit in said device.
In fact such signal processing circuits require a significantly larger space than the photo electro transducer unit itself, so that the advantage of miniaturization resulting from the drastically shortened optical path length in such elongated photo electro transducer unit cannot be fully exploited.
In order to resolve this difficulty, there has usually been employed a system of dividing the photo electro transducer elements or pixels into plural blocks, connecting these blocks in a matrix and utilizing signal processing circuits of an amount corresponding to one block for driving all these blocks in succession.
Such matrix wiring system is however associated with the drawback of so-called crosstalk phenomenon, in which the signal of a desired pixel is contaminated with the signal of other pixels. This crosstalk phenomenon is usually prevented by the use of matrix diodes respectively connected in series with the photo electro transducer elements.
In such method, the electric signal obtained in response to the optical signal received by the photoreceptor face of the photo electro transducer element is supplied to the signal processing circuit while the crosstalk-preventing diode connected in series to said element is electrically biased to show the forward characteristic.
In general such crosstalk-preventing diode is required to have an inverse resistance, i.e. resistance under an inverse bias, approximately 100 times larger than the light resistance, i.e. resistance under light irradiation, of the photo electro transducer element, although this ratio is considerably dependent on the signal accumulating time.
Consequently in case the photo electro transducer element is made from a material with a relatively low charge mobility (0.01-10 cm.sup.2 /V.multidot.sec) and is required to be of a high sensitivity, said light resistance of the photo electro transducer element becomes inevitably high.
Accordingly the crosstalk-preventing diode is required to show a high inverse resistance, but it is extremely difficult to prepare the diodes of such characteristics.
In addition such photo electro transducer device utilizing the above-mentioned crosstalk-preventing diodes is associated with the electric matching and connections between each transducer element and the corresponding diode, particularly in case of a device with a large number of pixels and in case a high resolving power is required.